Immobilization of acrylamide-modified oligonucleotides by co-polymerization

A flexible chemistry for solid phase attachment of oligonucleotides is described. Oligonucleotides bearing 5'-terminal acrylamide modifications efficiently co-polymerize with acrylamide monomers to form thermally stable DNA-containing polyacrylamide co-polymers. Co-polymerization attachment is specific for the terminal acrylamide group. Stable probe-containing layers are easily fabricated on supports bearing exposed acrylic groups, including plastic microtiter plates and silanized glass. Attachment can be accomplished using standard polyacrylamide gel recipes and polymerization techniques. Supports having a high surface density of hybridizable oligonucleotide (approximately 200 fmol/mm2) can be produced.     

Diode-loaded dipole antenna modeling and design

A circuit model for a diode-loaded dipole electric field measurement probe which is valid for frequencies below 10 GHz is presented. Assumptions are made to allow linear analysis based on the Laplace transform method. Optimized design criteria for the probe are then developed, with the major considerations being large bandwidth, independence of temperature, and maximum output. Experimental measurements on a probe designed for operation between 1 and 1000 MHz and comparison with the theoretical results are presented     

Performance evaluation of baseband OOK for wireless indoor infraredLAN's operating at 100 Mb/s

We investigate 100 Mb/s wireless nondirectional infrared communication in the indoor environment using baseband nonreturn-to-zero (NRZ) on-off keying (OOK) modulation. We show that intersymbol interference induced by multipath propagation impairs detection efficiency. Analytical and simulation results on specific channels demonstrate that an adaptive decision-feedback equalizer adapted according to the least-mean-squares algorithm recovers most of the performance degradation. We also evaluate the performance of a timing-recovery phase-locked loop operating independent of the adaptive equalizer; showing that it quickly and accurately determines the sampling phase with negligible performance degradation. We discuss effective methods of mitigating low-frequency noise induced by fluorescent lighting. We present a packet-based communication method and describe its features and performance. Our results support the feasibility of communication at 100 Mb/s over the infrared channel     

Performance of pulse-position modulation on measured non-directedindoor infrared channels

We examine the performance of pulse-position modulation (PPM) on measured channels with intersymbol interference (ISI). We summarize the bit-error-rate performance of unequalized systems and review the performance of maximum-likelihood sequence detection (MLSD) for PPM over ISI channels with additive white Gaussian noise. We evaluate the performance of PPM links over 46 experimentally measured indoor infrared channels. Detailed results are presented for 2, 4, 8, and 16-PPM at bit rates of 10 Mb/s and 30 Mb/s, and these techniques are compared to on-off keying. Our results show that when MLSD is employed, 16-PPM provides the best average-power efficiency among the modulation techniques considered in this study     

Electromagnetic coaxial railgun

Key design parameters of railguns are examined, namely, the inductance gradient, current distribution, electromagnetic pulses distribution and rail separation forces. A comparison of coaxial and parallel railguns indicates that the coaxial system has some advantages and should be considered during system design tradeoffs for an orbiting space probe launcher. It is suggested that an orbiting launcher could be used to send small and relatively inexpensive probes towards the planets and asteroid belt. A small, low-energy capacitor-powered coaxial railgun designed and built to demonstrate the armature acceleration and absence of the electromagnetic pulse forward of the armature is described     

Exact solution for the diffusion of a charged particle in a time-varying electromagnetic field

An exact solution for a charged particle which diffuses in a time-varying electromagnetic field has been determined by writing the equation of the charged particle in a matrix form and diagonalising the magnetic-field vector. Thus the components of the equation of motion are decoupled. A simple example is presented to show the significance of the results.     

Decision-feedback equalization of pulse-position modulation onmeasured nondirected indoor infrared channels

We examine the performance of two decision-feedback equalizers (DFEs) for pulse-position modulation (PPM) on measured nondirected indoor infrared channels with intersymbol interference. PPM offers high average-power efficiency, but on ISI channels, unequalized PPM suffers severe performance penalties. We have previously examined the performance of the maximum-likelihood sequence detector (MLSD), and found that it yields significant improvements. However, the MLSD often requires such large complexity and delay that it may be impractical. We investigate suboptimal, reduced-complexity equalization techniques for PPM, providing a performance analysis of zero-forcing chip-rate and symbol-rate DFEs. Our results show that a symbol-rate DFE provides performance that closely approaches that of the optimal MLSD     

Numerical analysis technique for diode-loaded dipole antennas

A circuit model for a double-loaded dipole electric field measurement probe that is valid for frequencies below 10 GHz is developed. A nonnegligible dipole radius and the nonlinear characteristics of the diode are taken into consideration. The dipole lumped-circuit elements and diode capacitances are determined by theoretical means, while the diode V-I characteristics and resistance are determined by a combined theoretical and empirical approach. Newton's iteration method is used to numerically solve the resulting nonlinear differential equation. Experimental measurements on a probe designed for operation between 1 and 1000 MHz are reported and compared with the theoretical results     

Trellis-coded pulse-position modulation for indoor wirelessinfrared communications

We analyze the performance of trellis-coded pulse-position modulation (PPM) on indoor, wireless infrared channels. We show that maximum-likelihood sequence detection (MLSD) of trellis-coded PPM is very effective in mitigating the multipath dispersion on such channels. We present code search results for high constraint-length, rate-2/3, 8-PPM and rate-3/4, 16-PPM codes. We provide bit-error rate curves and intersymbol interference power-penalties for MLSD of PPM with these codes, evaluated on ceiling-bounce channel models with delay spread per bit duration ratios of 0.01-0.3. Finally, we present Monte Carlo simulation results to verify our analysis     

Metropolitan-scale Wi-Fi mesh networks

Standardization, widespread vendor adoption, low cost, and ease of use have all contributed to the explosive growth in Wi-Fi (IEEE 802.11) wireless broadband networks. Wi-Fi access is now available on most notebook computers and personal digital assistants. However, the limited reach of Wi-Fi propagation and high cost of installing and maintaining a wired network backhaul connection have limited Wi-Fi network deployments to homes, offices, public hot spots, and some wide-area hot zones. In addition, installing, managing, and scaling multiple hot spots is difficult. Dense-cellular Wi-Fi mesh networking has the potential to bridge this digital divide, foster economic development, increase public safety organizations' efficiency and effectiveness, and connect communities. The technology is making it possible, for the first time, to create truly unwired cities.